Molecular Vision 2014; 20:970-976 <http://www.molvis.org/molvis/v20/970>
Received 12 December 2013 | Accepted 30 June 2014 | Published 02 July 2014

Aqueous humor erythropoietin levels in open-angle glaucoma patients with and without TTR V30M familial amyloid polyneuropathy

João M. Beirão,1,2,3 Luciana M. Moreira,3,4 João C. Oliveira,5 Maria J. Menéres,1,3 Bernardete B. Pessoa,1 Maria E. Matos,3 Paulo P. Costa,3,4 Paulo A. Torres,1,3 Idalina B. Beirão2,3

1Ophthalmology, Hospital de Santo António, Porto; 2Unidade Clínica de Paramiloidose, Hospital de Santo António, Porto; 3UMIB, ICBAS, Instituto de Ciências Biomédicas Abel Salazar, Porto; 4INSA Dr. Ricardo Jorge, Porto; 5Biochemistry Service, Hospital Santo António, Porto

Correspondence to: Melo Beirão, Serviço de Oftalmologia, Hospital de Santo António, Largo Prof. Abel Salazar, 2, 4099-001 Porto, Portugal; Phone: +351966009826; FAX: + 351 22 606 61 06; email: bbeirao@iol.pt

Abstract

Purpose: Glaucoma is the leading cause of irreversible blindness in familial amyloidotic polyneuropathy (FAP) patients. Erythropoietin (EPO) is a cytokine that has been shown to play a role in neuroprotection and is endogenously produced in the eye. EPO levels in the aqueous humor are increased in eyes with glaucoma. In this study, we evaluated the EPO concentration in the aqueous humor of FAP and non-FAP patients, with and without glaucoma.

Methods: Undiluted aqueous humor samples were obtained from 42 eyes that underwent glaucoma surgery, phacoemulsification, or vitrectomy. EPO concentration in the aqueous humor and blood were measured using the Immulite 2000 Xpi using an automatic analyzer (Siemens Healthcare Diagnostics).

Results: The mean EPO concentration in the aqueous humor of non-FAP glaucoma eyes group 2 (75.73±13.25 mU/ml) was significantly higher than non-FAP cataract eyes (17.22±5.33 mU/ml; p<0.001), FAP glaucoma eyes (18.82±10.16 mU/ml; p<0.001), and FAP nonglaucoma eyes (20.62±6.22 mU/ml; p<0.001). There was no statistically significant difference between FAP nonglaucoma eyes versus non-FAP cataract eyes (p = 0.23) and FAP glaucoma eyes versus FAP nonglaucoma eyes (p = 0.29). In the glaucoma groups, there was no correlation between the aqueous humor EPO concentration and the ocular pressure (p = 0.95) and mean deviation (p = 0.41). There was no correlation between the EPO serum concentration and EPO aqueous humor concentration in our patients (p = 0.77).

Conclusions: Unlike other glaucomatous patients, FAP patients with glaucoma do not show increased and potentially neuroprotective endocular EPO production in the aqueous humor and may need more aggressive glaucoma management.

Introduction

Glaucoma is a progressive optic nerve neuropathy and the major cause of preventable and irreversible blindness worldwide. It is characterized by visual field defects and nerve head cupping due to the loss of retinal ganglion cells [1]. Despite its multifactorial genesis [2-4], the major risk factor for glaucoma progression is the elevated intraocular pressure (IOP) [5,6], which compresses the retinal ganglion cells at the optic nerve head [7]. The only treatment that slows glaucoma progression involves lowering the IOP [8].

Familial amyloid polyneuropathy (FAP) is caused by the extracellular deposition of amyloid fibrils of mutant transthyretin (TTR) V30M in various tissues and organs [9-11]. TTR V30M mutation is the most common form of transthyretin amyloidosis (ATTR) variant in Portugal as well as in the world [12]. The main clinical expression of FAP disease is a sensorimotor and autonomic neuropathy, but other manifestations, such as nephropathy and hematologic and ocular abnormalities can occur. Among the reported ocular FAP complications [13-15], glaucoma is the major cause of irreversible vision loss and is often difficult to control [16].

Erythropoietin (EPO) was identified as a hematopoietic cytokine that promotes proerythroblast survival and maturation [17]. Recently, EPO was recognized as a member of the cytokine type 1 superfamily with multiple functions outside the bone marrow [18]. It provides direct protection against hypoxia by its anti-apoptotic, anti-oxidative, and anti-inflammatory properties and for its angiogenic capacity that allows the oxygen supply to ischemic tissues. Several studies have found that EPO protects photoreceptor cells, retinal ganglion cells, and retinal pigment epithelial cells from apoptosis [19-26]. Hernandez et al. [27] suggested that EPO is produced locally in the retina. Muller cells and retinal pigment epithelium were identified by Fu et al. [28] and Garcia-Ramírez et al. [29], respectively, as the cells responsible for EPO production in the eye.

Previous studies have shown a significantly increased EPO concentration in the aqueous humor of eyes with glaucoma [30-32]; this is probably a defence mechanism against glaucomatous damage [33] caused by hypoxia, ischemia, oxidative stress, and reduced pro-inflammatory cytokine production [34-39]. Although hypoxia/ischemia is the major stimulus for endocular and systemic EPO production [21,40-43], other incompletely understood factors may be involved [27,29].

FAP patients and even presymptomatic carriers have an inappropriately low EPO production [44]. In vitro studies suggest that the dissociated mutant TTR that polymerizes into misfolding amyloidogenic intermediates, protofilaments, and nonfibrillar aggregates of TTR rather than mature amyloid fibrils may induce cellular toxicity [45,46]. We propose that these amyloid precursors may be toxic to EPO-producing cells. This study was performed to evaluate the ocular EPO response in FAP patients with glaucoma.

Methods

It was recruited 42 eyes of 42 patients (18 females) with a mean age of 56.8±7.4 years. A prospective, controlled, nonrandomized, nonblind comparative study was conducted from January 2008 to December 2011 at the Ophthalmic and Clinical Chemistry Departments from Centro Hospitalar do Porto, Porto. Written informed consent was obtained from all patients. This study was performed in accordance with the Declaration of Helsinki of the World Medical Association and was approved by the Ethics Committee of the Centro Hospitalar do Porto.

Presurgical assessment included Snellen best-corrected visual acuity (Snellen chart, Takagi chart projector CP-30, calibrated for approximately 6 m), slit-lamp biomicroscopy, intraocular pressure (IOP) measurement by Goldman applanation tonometry (same person with AT-900 tonometer; Haag-Streit, Koniz, Switzerland), fundoscopy (90 D noncontact slit-lamp lens; Volk Optical, Mentor, OH), Humphrey perimetry (Humphrey Field Analyzer; Humphrey Instruments, San Leandro, CA), and the cup/disc ratio. All examinations were performed within 2 weeks before the surgical procedure.

Exclusion criteria for all groups were: previous laser and/or intraocular surgery; history of systemic (e.g., diabetes mellitus, kidney disease, cardiovascular disorders, anemia, immune disease, except FAP in groups 1 and 3) or any ocular disorders (e.g., age-related macular degeneration); history of medications that could influence the level of EPO (e.g., iron preparations, chemotherapeutic agents, granulocyte colony-stimulating factor, or systemic therapy with EPO), and patients with any type of glaucoma except open-angle glaucoma, such as angle-closure, pigmented, exfoliation, normotensive, and neovascular glaucomas, or ocular hypertension.

To clarify the relationship between aqueous EPO production and circulating blood EPO levels, we compared the aqueous and serum concentrations of EPO. Aqueous humor samples were obtained from each eye before the beginning of surgery (trabeculectomy, phacoemulsification, or vitrectomy). The standard procedure involved collecting undiluted aqueous humor samples (50–150 µl) through a paracentesis, using a 30-gauge needle on a tuberculin syringe under an operating microscope. Samples were obtained carefully to avoid touching intraocular tissues or blood contamination. All samples were carefully protected from light and were sent immediately to the laboratory for EPO measurement. At the same time, 9 ml of venous blood samples were collected in EDTA tubes from an antecubital vein immediately before sugery. The blood was immediately centrifuged and the blood serum put on the automatic analyzer.

Serum samples were obtained from the centrifugation of the blood sample. The samples of aqueous humor and serum had the same processing routine analysis. Serum and aqueous humor EPO concentrations were measured by a chemiluminescent method in an automatic Xpi Immulite 2000 analyzer (Siemens Healthcare Diagnostics, Siemens AG, Munich, Germany).

Statistical analysis

Statistical analysis was performed using nonparametric tests. The Kruskal–Wallis test was used to compare the groups in relation to age, and the chi-square test was used in relation to gender. The Mann–Whitney U test was used to compare the nonglaucoma, glaucoma, and FAP groups in relation to aqueous humor EPO and serum EPO levels. The relation between EPO and serum was evaluated by Spearman correlation. Values of p<0.05 were considered statistically significant. Data analysis was performed using IBM SPSS Statistics software version 20.

Results

A total of 21 glaucomatous eyes from 21 patients and 21 control eyes (21 patients) were enrolled in the study. The demographic characteristics of the patients are summarized in Table 1. Of the glaucoma eyes, ten were from FAP patients (group 1, mean age 55.4±10.0 years mean and standard deviation; five females) and 11 were from non-FAP patients (group 2, mean age 55.8±7.0 years mean and standard deviation; four females). Of the 21 control eyes, nine were from FAP patients with an indication for vitrectomy due to amyloid deposition (group 3, 55.9±8.5 years mean and standard deviation; four females) and 12 were from non-FAP patients awaiting phacoemulsification and intraocular lens implantation (group 4, 58.8±4.9 years mean and standard deviation; five females). Groups 1 and 2 presented indications for trabeculectomy, had uncontrolled IOP (defined as IOP higher than the target pressure with maximally topical antiglaucoma medications: prostaglandin + beta blocker + anhydrase carbonic inhibitor + alpha-2 agonist), abnormal visual field test results, and abnormal cup/disc ratio.

The ages and gender distribution of the patients were similar between groups (Kruskal–Wallis test, p = 0.56; chi-square test, p = 0.94). All FAP patients had received an orthotopic liver transplant.

As summarized in Table 2, the mean EPO concentration in the aqueous humor of nonglaucomatous eyes (group 3 versus group 4) was not significantly different between FAP and non-FAP patients (20.62±6.22 mU/ml in group 3 and 17.22±5.33 mU/ml in group 4, p = 0.23) and corresponds presumably to the basal ocular production of EPO. In the presence of glaucoma, EPO concentrations in the aqueous humor showed a significant increase in the non-FAP group (group 2, 75.73±13.25 mU/ml; group 1, 18.82±10.16 mU/ml; p<0.001), and when we compared the non-FAP glaucoma group (group 2) with the nonglaucoma groups (FAP group 3 and non-FAP group 4), a similar finding was observed (p<0.001) (Table 2). In the FAP groups (group 1 and group 3), we observed no significant difference between the mean EPO values ​​of patients with or without uncontrolled glaucoma (p = 0.29). As listed in Table 3, FAP patients with glaucoma (group 1) and non-FAP patients with glaucoma (group 2) were comparable in terms of the IOP (p = 0.39) and mean deviation (p = 0.75). The correlation between the IOP and the aqueous humor EPO was not significant in group 1 (mean IOP 26.20±1.93 mmHg; rs = 0.02, p = 0.95) and group 2 (mean IOP 26.82±1.72 mmHg; rs = 0.27, p = 0.41). There was also no significant correlation between the mean deviation and the aqueous humor EPO in group 1 (rs = –0.48, p = 0.16) or group 2 (rs = –0.07, p = 0.83).

Serum EPO levels among patient groups were not significantly different when multiple testing was taken into account (Bonferroni correction). No statistically significant correlation between the values ​​of EPO in the serum and in the aqueous humor was observed in any patient (Spearman correlation coefficient r = 0.047, p = 0.77).

Discussion

Glaucoma is a manifestation of a heterogeneous group of diseases with a very complex and multifactorial pathophysiology [8]. Although hypotensive therapy is today the only possible therapeutic intervention, neuroprotective treatment strategies are emerging as a result of the advances in the comprehension of the pathophysiological mechanisms of glaucoma. In the future, neuroprotective agents will probably be part of the therapeutic arsenal available for the treatment of glaucoma. EPO has been shown to have a protective effect on ganglion cells against acute ischemia injury [28,47] and has been proposed as a potential neuroprotective treatment.

In this study we confirmed that the aqueous humor EPO level is higher in glaucomatous eyes than in nonglaucomatous eyes with cataracts, as previously reported [30-32,48,49]. This increase in aqueous humor EPO levels could be a result of local production and/or active transport through the blood–ocular barrier. This observation lends support to the hypothesis that EPO acts as an endogenous neuroprotector of retinal ganglion cells [19].

In spite of the inappropriately low renal EPO production reported in FAP ATTR V30M [44], its basal level in the aqueous humor of FAP patients was not significantly altered. However, FAP patients seemed to be unable to increase endocular EPO production in the presence of glaucoma. In previous studies, we showed an inappropriate secretion of renal EPO in FAP and an inability to increase EPO production in response to decreased serum hemoglobin levels, leading to a high incidence of anemia in these patients. The lack of response to glaucoma in FAP patients could be the ocular counterpart of the stunted renal EPO production in FAP in response to anemia.

It has been suggested that inhibition of EPO production could be caused by the toxicity of prefibrillar aggregates of TTR V30M [44,50,51]. These oligomers induce the expression of oxidative stress, pro-inflammatory cytokines, and apoptosis-related molecules [52,53] through the binding of TTR aggregates to the receptor for advanced glycation end products, activation of extracellular signal-regulated kinase cascades, and nuclear transcription factor kB [52-56], suppressing the EPO production. All our FAP patients had previously received an orthotopic liver transplant to eliminate their main source of mutant TTR, their own liver [57]. After liver transplantation, mutant TTR is removed from systemic circulation; however, its local production in the eye remains presumably unaffected. Therefore, the ocular pathology related to FAP, which includes glaucoma, continues to progress after liver transplantation; presumably there is also continuing deposition of cytotoxic prefibrillar TTR aggregates.

Garcia-Ramirez found that other factors besides hypoxia-inducible factors (HIF)-mediated hypoxia might be important in the upregulation of EPO. Hypoxia, ischemia, elevated reactive oxygen species, or increases in glutamate and nitric oxide caused by glaucomatous damage are probably the cause of elevated aqueous humor EPO concentration in chronic glaucoma [30]. The pro-inflammatory cytokines interleukin (IL)-1, IL-6, interferon-γ, and tumor necrosis factor (TNF)-α inhibit EPO production [58,59], but despite being increased in the aqueous humor of glaucoma eyes, as is especially the case for TNF-α [60], these cytokines do not prevent an increase in EPO levels.

Increased levels of TTR in the aqueous humor of glaucoma patients have been documented [61-63]. If glaucoma leads to an increase expression of TTR in the aqueous humor, an increased concentration of the unstable TTR V30M in FAP patients’ eyes could contribute to the increased development of a mechanical barrier to the outflow of the aqueous humor [64], resulting in worsening the glaucoma. The association of open-angle glaucoma with autonomic nervous system dysfunction suggests that this could also play a role in the pathogenesis of the disease [65]. Patients with systemic sympathetic and parasympathetic neuropathies have a higher incidence of open-angle and normal-pressure glaucoma [66-69]. Because FAP patients have an early onset neuropathy with markedly autonomic involvement, it is likely that autonomic dysfunction plays a role in glaucoma pathophysiology. Other possible contributing factors are the hemodynamic instability often presented in FAP patients due to vascular deregulation and abnormal blood pressure that may compound the harmful effects of glaucoma, particularly during sleep [65].

In the groups with glaucoma, there was no correlation between the aqueous humor EPO concentration and the values ​​of IOP and mean deviation. It seems that the concentration of EPO in the aqueous humor is not related to the IOP in eyes with glaucoma or previous eye injury caused by glaucoma.

In this study, patients with pseudoexfoliative and uveitic glaucomas were excluded because some studies pointed to blood–aqueous humor barrier breakdown in these situations [70,71]. EPO can cross the blood–brain barrier and blood–retina barrier [41]. We did not found a significant correlation between aqueous humor and serum EPO concentrations as other authors have found [30,31]. The elevation of the aqueous humor EPO level in glaucoma was not associated with a parallel increase in blood EPO levels, corroborating the role of local EPO production as already proposed by Fu [28] and Garcia-Ramirez [29].

In conclusion, our study confirmed that the level of EPO is increased in aqueous humor of open-angle glaucomatous eyes, as found by other authors. This increase was not observed in FAP patients. With the increased survival of transplanted FAP patients, glaucoma prevalence is expected to increase dramatically with increased suvival of the transplanted patients. We showed lower endogenous neuroprotection in glaucomatous eyes of FAP patients, emphasizing the need for more aggressive glaucoma management to maintain vision through life.

References

  1. Agar A, Yip SS, Hill MA, Coroneo MT. Pressure related apoptosis in neuronal cell lines. J Neurosci Res. 2000; 60:495-503. [PMID: 10797552]
  2. Flammer J, Orgül S. Optic nerve blood-flow abnormalities in glaucoma. Prog Retin Eye Res. 1998; 17:267-89. [PMID: 9695795]
  3. Cioffi GA. Ischemic model of optic nerve injury. Trans Am Ophthalmol Soc. 2005; 103:592-613. [PMID: 17057819]
  4. Tezel G, Wax MB. Hypoxia-inducible factor 1alpha in the glaucomatous retina and optic nerve head. Arch Ophthalmol. 2004; 122:1348-56. [PMID: 15364715]
  5. Evans DW, Hosking SL, Gherghel D, Bartlett JD. Contrast sensitivity improves after brimonidine therapy in primary open angle glaucoma: a case for neuroprotection. Br J Ophthalmol. 2003; 87:1463-5. [PMID: 14660453]
  6. Gordon MO, Beiser JA, Brandt JD, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller JP, Parrish RK, , 2nd Wilson MR, Kass MA. The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002; 120:714-20. [PMID: 12049575]
  7. Izzotti A, Bagnis A, Saccà SC. The role of oxidative stress in glaucoma. Mutat Res. 2006; 612:105-14. [PMID: 16413223]
  8. Leske MC, Heijl A, Hussein M, Bengtsson B, Hyman L, Komaroff E, Early Manifest Glaucoma Trial Group. Factors for glaucoma progression and the effect of treatment: the early manifest glaucoma trial. Arch Ophthalmol. 2003; 121:48-56. [PMID: 12523884]
  9. Saraiva MJ, Costa PP, Goodman DS. Studies on plasma transthyretin (prealbumin) in familial amyloidotic polyneuropathy, Portuguese type. J Lab Clin Med. 1983; 102:590-603. [PMID: 6311926]
  10. Saraiva MJ, Costa PP, Birken S, Goodman DS. Presence of an abnormal transthyretin (prealbumin) in Portuguese patients with familial amyloidotic polyneuropathy. Trans Assoc Am Physicians. 1983; 96:261-70. [PMID: 6208668]
  11. Saraiva MJ, Birken S, Costa PP, Goodman DS. Amyloid fibril protein in familial amyloidotic polyneuropathy, Portuguese type. Definition of molecular abnormality in transthyretin (prealbumin). J Clin Invest. 1984; 74:104-19. [PMID: 6736244]
  12. Ando Y, Araki S, Ando M. Transthyretin and familial amyloidotic polyneuropathy. Intern Med. 1993; 32:920-2. [PMID: 8204970]
  13. Ando E, Ando Y, Okamura R, Uchino M, Ando M, Negi A. Ocular manifestations of familial amyloidotic polyneuropathy type I: long-term follow up. Br J Ophthalmol. 1997; 81:295-8. [PMID: 9215058]
  14. Sandgren O, Kjellgren D, Suhr OB. Ocular manifestations in liver transplant recipients with familial amyloid polyneuropathy. Acta Ophthalmol (Copenh). 2008; 86:520-4. [PMID: 18435819]
  15. Beirão M, Matos E, Beirão I, Costa PP, Torres P. Anticipation of presbyopia in Portuguese familial amyloidosis ATTR V30M. Amyloid. 2011; 18:92-7. [PMID: 21591979]
  16. Kimura A, Ando E, Fukushima M, Koga T, Hirata A, Arimura K, Ando Y, Negi A, Tanihara H. Secondary glaucoma in patients with familial amyloidotic polyneuropathy. Arch Ophthalmol. 2003; 121:351-6. [PMID: 12617705]
  17. Jelkmann W. Erythropoietin: structure, control of production, and function. Physiol Rev. 1992; 72:449-89. [PMID: 1557429]
  18. Ghezzi P, Brines M. Erythropoietin as an antiapoptotic, tissue-protective cytokine. Cell Death Differ. 2004; 11Suppl 1:S37-44. [PMID: 15243580]
  19. Becerra SP, Amaral J. Erythropoietin - an endogenous retinal survival factor. N Engl J Med. 2002; 347:1968-70. [PMID: 12477950]
  20. Dreixler JC, Hagevik S, Hemmert JW, Shaikh AR, Rosenbaum DM, Roth S. Involvement of erythropoietin in retinal ischemic preconditioning. Anesthesiology. 2009; 110:774-80. [PMID: 19322943]
  21. Inomata Y, Hirata A, Takahashi E, Kawaji T, Fukushima M, Tanihara H. Elevated erythropoietin in vitreous with ischemic retinal diseases. Neuroreport. 2004; 15:877-9. [PMID: 15073535]
  22. Sakanaka M, Wen TC, Matsuda S, Masuda S, Morishita E, Nagao M, Sasaki R. In vivo evidence that erythropoietin protects neurons from ischemic damage. Proc Natl Acad Sci USA. 1998; 95:4635-40. [PMID: 9539790]
  23. Tsai JC, Song BJ, Wu L, Forbes M. Erythropoietin: a candidate neuroprotective agent in the treatment of glaucoma. J Glaucoma. 2007; 16:567-71. [PMID: 17873720]
  24. Tsai JC, Wu L, Worgul B, Forbes M, Cao J. Intravitreal administration of erythropoietin and preservation of retinal ganglion cells in an experimental rat model of glaucoma. Curr Eye Res. 2005; 30:1025-31. [PMID: 16282136]
  25. Villa P, Bigini P, Mennini T, Agnello D, Laragione T, Cagnotto A, Viviani B, Marinovich M, Cerami A, Coleman TR, Brines M, Ghezzi P. Erythropoietin selectively attenuates cytokine production and inflammation in cerebral ischemia by targeting neuronal apoptosis. J Exp Med. 2003; 198:971-5. [PMID: 12975460]
  26. Wang ZY, Shen LJ, Tu L, Hu DN, Liu GY, Zhou ZL, Lin Y, Chen LH, Qu J. Erythropoietin protects retinal pigment epithelial cells from oxidative damage. Free Radic Biol Med. 2009; 46:1032-41. [PMID: 19136057]
  27. Hernández C, Fonollosa A, García-Ramírez M, Higuera M, Catalán R, Miralles A, García-Arumí J, Simó R. Erythropoietin is expressed in the human retina and it is highly elevated in the vitreous fluid of patients with diabetic macular edema. Diabetes Care. 2006; 29:2028-33. [PMID: 16936148]
  28. Fu QL, Wu W, Wang H, Li X, Lee VW, So KF. Up-regulated endogenous erythropoietin/erythropoietin receptor system and exogenous erythropoietin rescue retinal ganglion cells after chronic ocular hypertension. Cell Mol Neurobiol. 2008; 28:317-29. [PMID: 17554621]
  29. García-Ramírez M, Hernández C, Simó R. Expression of erythropoietin and its receptor in the human retina: a comparative study of diabetic and nondiabetic subjects. Diabetes Care. 2008; 31:1189-94. [PMID: 18332162]
  30. Cumurcu T, Bulut Y, Demir HD, Yenisehirli G. Aqueous humor erythropoietin levels in patients with primary open-angle glaucoma. J Glaucoma. 2007; 1:645-8.
  31. Wang ZY, Zhao KK, Zhao PQ. Erythropoietin is increased in aqueous humor of glaucomatous eyes. Curr Eye Res. 2010; 35:680-4. [PMID: 20673044]
  32. Mokbel TH, Ghanem AA, Kishk H, Arafa LF, El-Baiomy AA. Erythropoietin and soluble CD44 levels in patients with primary open-angle glaucoma. Clin Experiment Ophthalmol. 2010; 38:560-5. [PMID: 20456444]
  33. Dirnagl U, Simon RP, Hallenbeck JM. Ischemic tolerance and endogenous neuroprotection. Trends Neurosci. 2003; 26:248-54. [PMID: 12744841]
  34. Wenger RH. Cellular adaptation to hypoxia: O2-sensing protein hydroxylases, hypoxia-inducible transcription factors, and O2-regulated gene expression. FASEB J. 2002; 16:1151-62. [PMID: 12153983]
  35. Arjamaa O, Nikinmaa M. Oxygen-dependent diseases in the retina: role of hypoxia-inducible factors. Exp Eye Res. 2006; 83:473-83. [PMID: 16750526]
  36. Silva M, Grillot D, Benito A, Richard C, Nuñez G, Fernández-Luna JL. Erythropoietin can promote erythroid progenitor survival by repressing apoptosis through Bcl-XL and Bcl-2. Blood. 1996; 88:1576-82. [PMID: 8781412]
  37. Sakanaka M, Wen TC, Matsuda S, Masuda S, Morishita E, Nagao M, Sasaki R. In vivo evidence that erythropoietin protects neurons from ischemic damage. Proc Natl Acad Sci USA. 1998; 95:4635-40. [PMID: 9539790]
  38. Kawakami M, Sekiguchi M, Sato K, Kozaki S, Takahashi M. Erythropoietin receptor-mediated inhibition of exocytotic glutamate release confers neuroprotection during chemical ischemia. J Biol Chem. 2001; 276:39469-75. [PMID: 11504731]
  39. Genc S, Koroglu TF, Genc K. Erythropoietin as a novel neuroprotectant. Restor Neurol Neurosci. 2004; 22:105-19. [PMID: 15272145]
  40. Fisher JW. Erythropoietin: physiology and pharmacology update. Exp Biol Med (Maywood). 2003; 228:1-14. [PMID: 12524467]
  41. Grimm C, Wenzel A, Groszer M, Mayser H, Seeliger M, Samardzija M, Bauer C, Gassmann M, Remé CE. HIF-1-induced erythropoietin in the hypoxic retina protects against light-induced retinal degeneration. Nat Med. 2002; 8:718-24. [PMID: 12068288]
  42. Katsura Y, Okano T, Matsuno K, Osako M, Kure M, Watanabe T, Iwaki Y, Noritake M, Kosano H, Nishigori H, Matsuoka T. Erythropoietin is highly elevated in vitreous fluid of patients with proliferative diabetic retinopathy. Diabetes Care. 2005; 28:2252-4. [PMID: 16123502]
  43. Watanabe D, Suzuma K, Matsui S, Kurimoto M, Kiryu J, Kita M, Suzuma I, Ohashi H, Ojima T, Murakami T, Kobayashi T, Masuda S, Nagao M, Yoshimura N, Takagi H. Erythropoietin as a retinal angiogenic factor in proliferative diabetic retinopathy. N Engl J Med. 2005; 353:782-92. [PMID: 16120858]
  44. Beirão I, Lobato L, Costa PM, Fonseca I, Mendes P, Silva M, Bravo F, Cabrita A, Porto G. Kidney and anemia in familial amyloidosis type I. Kidney Int. 2004; 66:2004-9. [PMID: 15496172]
  45. Bucciantini M, Calloni G, Chiti F, Formigli L, Nosi D, Dobson CM, Stefani M. Prefibrillar amyloid protein aggregates share common features of cytotoxicity. J Biol Chem. 2004; 279:31374-82. [PMID: 15133040]
  46. Reixach N, Deechongkit S, Jiang X, Kelly JW, Buxbaum JN. Tissue damage in the amyloidoses: Transthyretin monomers and nonnative oligomers are the major cytotoxic species in tissue culture. Proc Natl Acad Sci USA. 2004; 101:2817-22. [PMID: 14981241]
  47. Junk AK, Mammis A, Savitz SI, Singh M, Roth S, Malhotra S, Rosenbaum PS, Cerami A, Brines M, Rosenbaum DM. Erythropoietin administration protects retinal neurons from acute ischemia-reperfusion injury. Proc Natl Acad Sci USA. 2002; 99:10659-64. [PMID: 12130665]
  48. Nassiri N, Nassiri N, Majdi M, Mehrjardi HZ, Shakiba Y, Haghnegahdar M, Heidari AB, Djalilian AR, Mirahmadian M. Erythropoietin levels in aqueous humor of patients with glaucoma. Mol Vis. 2012; 18:1991-5. [PMID: 22876126]
  49. Hamid M, Fahmy I, Moemen L, El-Beltagy T. Role of matrix metalloproteinase-2 and its inhibitor and erythropoietin in the pathogenesis of pseudoexfoliative glaucoma. Australian J Bas Appl Sci . 2008; 2:752-6.
  50. Beirão I, Moreira L, Porto G, Lobato L, Fonseca I, Cabrita A, Costa PM. Low erythropoietin production in familial amyloidosis TTR V30M is not related with renal congophilic amyloid deposition. A clinicopathologic study of twelve cases. Nephron Clin Pract. 2008; 109:c95-9. [PMID: 18596378]
  51. Beirão I, Moreira L, Barandela T, Lobato L, Silva P, Gouveia CM, Carneiro F, Fonseca I, Porto G, Pinho E, Costa P. Erythropoietin production by distal nephron in normal and familial amyloidotic adult human kidneys. Clin Nephrol. 2010; 74:327-35. [PMID: 20979939]
  52. Sousa MM, Cardoso I, Fernandes R, Guimarães A, Saraiva MJ. Deposition of transthyretin in early stages of familial amyloidotic polyneuropathy: evidence for toxicity of nonfibrillar aggregates. Am J Pathol. 2001; 159:1993-2000. [PMID: 11733349]
  53. Fiszman ML, Di Egidio M, Ricart KC, Repetto MG, Borodinsky LN, Llesuy SF, Saizar RD, Trigo PL, Riedstra S, Costa PP, Villa AM, Katz N, Lendoire JC, Sica RE. Evidence of oxidative stress in familial amyloidotic polyneuropathy type 1. Arch Neurol. 2003; 60:593-7. [PMID: 12707074]
  54. Sousa MM, Du Yan S, Fernandes R, Guimaraes A, Stern D, Saraiva MJ. Familial amyloid polyneuropathy: receptor for advanced glycation end products-dependent triggering of neuronal inflammatory and apoptotic pathways. J Neurosci. 2001; 21:7576-86. [PMID: 11567048]
  55. Sousa MM, Yan SD, Stern D, Saraiva MJ. Interaction of the receptor for advanced glycation end products (RAGE) with transthyretin triggers nuclear transcription factor kB (NF-kB) activation. Lab Invest. 2000; 80:1101-10. [PMID: 10908156]
  56. Monteiro FA, Sousa MM, Cardoso I, do Amaral JB, Guimarães A, Saraiva MJ. Activation of ERK1/2 MAP kinases in familial amyloidotic polyneuropathy. J Neurochem. 2006; 97:151-61. [PMID: 16515552]
  57. Benson MD. Liver transplantation and transthyretin amyloidosis. Muscle Nerve. 2013; 47:157-62. [PMID: 23169427]
  58. Jelkmann W. Proinflammatory cytokines lowering erythropoietin production. J Interferon Cytokine Res. 1998; 18:555-9. [PMID: 9726435]
  59. Vannucchi AM, Grossi A, Rafanelli D, Statello M, Cinotti S, Rossi-Ferrini P. Inhibition of erythropoietin production in vitro by human interferon gamma. Br J Haematol. 1994; 87:18-23. [PMID: 7947242]
  60. Balaiya S, Edwards J, Tillis T, Khetpal V, Chalam KV. Tumor necrosis factor-alpha (TNF-α) levels in aqueous humor of primary open angle glaucoma. Clin Ophthalmol.. 2011; 5:553-6. [PMID: 21607023]
  61. Prata TS, Navajas EV, Melo LA, , Jr Martins JR, Nader HB, Belfort R, Jr. Aqueous humor protein concentration in patients with primary open-angle glaucoma under clinical treatment. Arq Bras Oftalmol. 2007; 70:217-20. [PMID: 17589689]
  62. Grus FH, Joachim SC, Sandmann S, Thiel U, Bruns K, Lackner KJ, Pfeiffer N. Transthyretin and complex protein pattern in aqueous humor of patients with primary open-angle glaucoma. Mol Vis. 2008; 14:1437-45. [PMID: 18682810]
  63. Inoue T, Kawaji T, Tanihara H. Elevated levels of multiple biomarkers of Alzheimer's disease in the aqueous humor of eyes with open-angle glaucoma. Invest Ophthalmol Vis Sci. 2013; 54:5353-8. [PMID: 23860758]
  64. Silva-Araújo AC, Tavares MA, Cotta JS, Castro-Correia JF. Aqueous outflow system in familial amyloidotic polyneuropathy, Portuguese type. Graefes Arch Clin Exp Ophthalmol. 1993; 231:131-5. [PMID: 8385054]
  65. Gherghel D, Hosking SL, Orgül S. Autonomic nervous system, circadian rhythms, and primary open-angle glaucoma. Surv Ophthalmol. 2004; 49:491-508. [PMID: 15325194]
  66. Brown CM, Dütsch M, Michelson G, Neundörfer B, Hilz MJ. Impaired cardiovascular responses to baroreflex stimulation in open-angle and normal-pressure glaucoma. Clin Sci (Lond). 2002; 102:623-30. [PMID: 12049615]
  67. Clark CV, Mapstone R. Systemic autonomic neuropathy in open-angle glaucoma. Doc Ophthalmol. 1986; 64:179-85. [PMID: 3608758]
  68. Kumar R, Ahuja VM. A study of changes in the status of autonomic nervous system in primary open angle glaucoma cases. Indian J Med Sci. 1999; 53:529-34. [PMID: 10862279]
  69. Riccadonna M, Covi G, Pancera P, Presciuttini B, Babighian S, Perfetti S, Bonomi L, Lechi A. Autonomic system activity and 24-hour blood pressure variations in subjects with normal- and high-tension glaucoma. J Glaucoma. 2003; 12:156-63. [PMID: 12671471]
  70. Küchle M, Nguyen NX, Hannappel E, Naumann GO. The blood-aqueous barrier in eyes with pseudoexfoliation syndrome. Ophthalmic Res. 1995; 27Suppl 1:136-42. [PMID: 8577452]
  71. Nguyen NX, Kuchle M, Naumann GO. Quantification of blood-aqueous barrier breakdown after phacoemulsification in Fuchs' heterochromic uveitis. Ophthalmologica. 2005; 219:21-5. [PMID: 15627823]